Federal officials are considering new Medicare Advantage rules to help protect seniors when insurers make significant reductions to their networks of doctors and other health care providers. The proposals follow UnitedHealthcare's decision to drop thousands of doctors from its Medicare Advantage plans in at least 10 states last fall. The government's response is part of the 148-page announcement of proposed rules and payment rates for next year's Medicare Advantage plans released last month by the U.S. Centers for Medicare & Medicaid Services. Officials say that the terminations only a few weeks before Medicare's Dec. 7 enrollment deadline may not have given seniors enough time to find new doctors, choose a different plan or rejoin traditional Medicare, which does not restrict beneficiaries to a limited network of providers.